1. Field of the Invention
The invention relates generally to the conversion of lipid-containing biomass, and more particularly to the conversion of lipid-containing biomass to liquid fuels and/or platform chemicals.
2. Description of the Related Art
Lipid-containing biomass is abundantly available. Many crops are grown for their oil content. The oil is recovered from the crop, generally by pressing. The oils are generally used for human food or animal feed. Examples of oil crops include olives, palm, flax seeds, sunflower seeds, and the like.
Crops producing oils having high levels of poly-unsaturated fatty acids have been used since antiquity for producing varnishes and lacquers. Due to their highly unsaturated nature such oils “harden” when exposed to oxygen in the air. These oils are in general not suitable for use as foods, because of their instability and unattractive taste.
In modern times oil crops have been grown for the production of so-called “biodiesel”. In Europe, extensive areas of arable land have been devoted to the cultivation of rapeseed in order to meet European Union targets for renewable energy resources. The use of valuable land for this purpose has met with strong opposition, as food shortages have begun to drive up food prices.
The production of vegetable food oils leaves significant amounts of residue. The residue typically comprises cellulose, protein, and a residual amount of lipid. The amount of oil that can be recovered from oil crops by pressing is limited, because high pressure pressing tends to contaminate the oil with other plant residues, which negatively impact the quality and the stability of the oil. Consequently, oil producing plants generate large amounts of biomass waste comprising significant amounts of lipids. These lipids may be removed by extraction, which requires the use of volatile organic chemicals (VOCs), the handling of which requires expensive equipment.
Another abundant source of lipid-containing biomass is algae. Algae are particularly attractive, because as a genus they convert solar energy to biomass far more efficiently than land-based plants. Moreover, many algae species thrive in salt or brackish water, thus avoiding the need for precious fresh water. The cultivation of algae is an attractive option for arid coastal areas, which have an abundant supply of solar energy and sea water.
Unlike land-based plants, algae contain little or no lignin. Pressing techniques as are used for the recovery of oils from land-based crops are in general not suitable for separating the oils from algae biomass. The cell walls are too weak to withstand the pressing action. In general, separating the lipids from the rest of the algae biomass requires an expensive process, which thus far has limited the use of algae crops.
Rayne et al., Rapid Dissolution of Lignocellulosic Plant Materials in Ionic Liquid, Nature Precedings hdl:10101/npre.2007.637.1, posted 7 Aug. 2007, reports on experiments with six different lignocellulosic materials. Dissolution limits for the six biomass types were approximately 5%. The ionic liquid used was 3,3′-ethane-1,2-diylbis(1-methyl-1H-imidazol-3ium. The biomass types were substantially lipid free.
United States Patent Application Publication 2006/0241287, published Oct. 26, 2006, discloses a method for using ionic liquids to extract and separate a biopolymer from a biomass containing the biopolymer. The examples relate to the dissolution of polyhydroxyalkanoate (PHA); the extraction of PHA from a biomass; and the dissolution and recovery of keratin. The ionic liquids are all organic.
Thus, there is a particular need for a process for the conversion of lipid-containing biomass. Preferably this process uses low cost biomass material as the feed. The process may be used to convert biomass to liquid fuel, and/or platform chemicals.